Ferrite_bainite_phase_steels
Steel grade designations
Information on application and processing
Forming
Despite its high strength, ferrite-bainite-phase steel displays good cold formability in general. The steel displays high work hardening even at slight strains. In cold cutting-to-size or flame cutting, hardening of the cut edges has to be expected. If these are subsequently cold formed, it may be necessary to stress relieve, machine or radius the edges in the bending zone. Ferrite-bainite-phase steel is not recommended for hot forming and hot leveling operations due to
p ossible effects on the mechanical properties.
Joining
Ferrite-bainite-phase steels can be welded to other ferrite-bainite-phase steels and to other
c ommon steel grades. The welding parameters must be matche
d to th
e material. To spot-weld ferrite-bainite-phase steels the same equipment can be used as for unalloyed deep-drawing steels. However the electrode forces should be increased slightly to achieve a large welding current range. When spot welding ferrite-bainite-phase steels the use o
f sturdy weldin
g tongs wit
h plenty of force reserves is recommended, which also offer advantages in the event of fit-up problems. Increasing the welding time also has a favorable effect on the welding current range, which is why medium and long welding times or – in accordance with EN ISO 8278-2 – multiple impulse welds are recommended for spot welding.
Welding range diagram of a ferrite-bainite-phase steel
Available shapes and sizes
FB-W? 450 and FB-W? 600, hot rolled thicknesses > 3 mm on request
Compared with deep-drawing steels, ferrite-bainite-phase steels tend to have lower electrical
c onductivity, which is why they require lower welding currents with the same electrode force in spot welding. When resistance spot welding galvanize
d sheets th
e welding currents must be raised due to the higher conductivity o
f the coatin
g compared wit
h the base metal. In addition, increasing the electrode force and welding time has a favorable effect on the welding current range. As well as sheet grade, surface and thickness combination, other factors such as the type of electrode used and type of welding current play an important role in determining the optimum joining parameters. The relationships shown in the figure are therefore to be seen as examples only.
The information sheet DVS 0938-2 “Arc brazing” describes the brazing of steels up to a tensile strength R m of approx. 500 MPa. As the material here is above this tensile strength it is advisable to check suitability for brazing depending on the part.
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General Note:
All statements as to the properties or utilization of the materials and products mentioned in this brochure are for the purpose of description only. Guarantees in respect of the existence of certain properties or utilization of the material mentioned valid are only if agreed upon in writing. Subject to technical changes without notice. Reprints, even extracts, only with permission of ThyssenKrupp Steel AG.
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